Google Web Toolkit (GWT) + Google App Engine (GAE) + Detached Data Persistence

Question

I would like to develop a web-app requiring data persistence using GWT and GAE. As I understand it, my only (or at least by far the most convenient) option for data persiste

Answer 1

Awhile ago I wrote a post Using an ORM or plain SQL?

This came up last year in a GWT application I was writing. Lots of translation from EclipseLink to presentation objects in the service implementation. If we were using ibatis it would've been far simpler to create the appropriate objects with ibatis and then pass them all the way up and down the stack. Some purists might argue this is Bad™. Maybe so (in theory) but I tell you what: it would've led to simpler code, a simpler stack and more productivity.

which basically matches your observation.

But of course that isn't an option with Google App Engine so you're pretty much stuck having a translation layer between client-side objects and your JPA entities.

JPA entities are quite rigid so they're not really appropriate for sending back and forth between the client anyway. Typically you want little bits from several entities when doing this (thus ending up with some sort of presentation-layer value object). That is your path forward.

Answer 2

Try this. It is a module for serializing GAE core types and send them to the GWT client.

Answer 3

I've been using Objectify as well, and I really like it. You still have to do some dancing around with pre/postLoad methods to translate e.g. Text to String and back.

Answer 4

What about directly using Datastore API to load/store POJO domain objects?

It should be comparable to DTO approach, meaning e.g. that you have to manually handle all fields (if you don't use tricks like reflection-based automation) while it should give you more flexibility and full access to all Datastore features.

Answer 5

I've recently found Objectify, which is designed to be a replacement for JDO. Not much experience with it yet but its simpler to use than JDO, seems more lightweight, and claims to get around the need for DTOs with GWT, though I haven't tried that particular feature yet.

Answer 6

I believe Google's official answer for this is GWT 2.1 RequestFactory. Given that you are using GWT and GAE, I'd suggest you stick to the official Google framework... I have a similar GWT / GAE based app and that's what I am doing.

By the way, setting up RequestFactory is a bit of pain in the ass. The current Eclipse plug-in doesn't include all the jars but I was able to find the help I needed, in Stackoverflow